The invention generally relates to a method of processing a semiconductor assembly. More particularly, the invention relates to a method of processing a semiconductor assembly suitable for use in photovoltaic devices with substrate configuration.
Thin film solar cells or photovoltaic devices typically include a plurality of semiconductor layers disposed on a transparent substrate, wherein one layer serves as a window layer and a second layer serves as an absorber layer. The window layer allows the penetration of solar radiation to the absorber layer, where the optical energy is converted to usable electrical energy. The window layer further functions to form a heterojunction (p-n junction) in combination with an absorber layer. The window layer desirably is thin enough and has a wide enough bandgap (2.4 eV or more) to transmit most available light through to the absorber layer.
Cadmium telluride/cadmium sulfide (CdTe/CdS) heterojunction-based photovoltaic cells are one such example of thin film solar cells, where CdS functions as the window layer. Typically, the CdTe/CdS-based photovoltaic cells include a superstrate configuration (formed by disposing the absorber layer on the window layer) or a substrate configuration (formed by disposing the window layer on the absorber layer).
However, thin film photovoltaic devices may suffer from low efficiency values because of one or both of low short-circuit current (JSC) or low open-circuit voltage (VOC). Typical methods to increase the JSC in superstrate configuration may however also adversely affect the VOC. Thus it may be desirable to alter the band gap profile of the absorber layer to increase the JSC without affecting the VOC.